Satellite navigation

Sat Nav

Foreign names, anagrams and trivia subject

Serious information

Sat nav systems allow electronic devices to determine their location within a few metres using time signals transmitted along a line of sight by radio from satellites in space. Receivers on the ground with a fixed position can also be used to calculate the precise time as a reference for scientific experiments. m. GPS is used for Military, Surveying, and Geocaching,

Unlike the GPS, GLONASS, and Galileo systems, which offer global positioning, Beidou uses satellites in geostationary orbit. This means that the system does not require a large constellation of satellites, but limits coverage to areas on Earth where satellites are visible.

China has also associated itself with the Galileo project. The Beidou navigation system is a project by the People's Republic of China in developing a independent satellite navigation system. Beidou is the Chinese name of the Ursa Major constellation.

Beidou 1A was launched on 30 October 2000 and Beidou 1B followed on 20 December 2000. China plans to complete the system with a second pair, and Beidou 2A was put into orbit on 24 May 2003.

An early predecessor were the ground based LORAN and Omega. which used terrestrial longwave radio transmitters instead of satellites. These systems broadcast a radio pulse from a known "master" location, followed by repeated pulses from a number of "slave" stations. The delay between the reception and sending of signal was carefully controlled, allowing the receivers to compare the delay between reception and the delay between sending.

The first satellite navigation system was Transit, a system deployed by the US military in the 1960s.

Modern systems are more direct. The satellite broadcasts a signal that contains the position of the satellite and the precise time the signal was transmitted. The position of the satellite is transmitted in a data message that is superimposed on a code that serves as a timing reference. The satellite uses an atomic clock to maintain synchronization of all the satellites in the constellation. Several such measurements can be made at the same time to different satellites, allowing a continual fix to be generated in real time.

Satellite navigation systems have a variety of civilian uses navigation, ranging from personal hand-held devices for trekking, to devices fitted to cars, trucks, ships and aircraft, synchronization, location-based services such as enhanced 911 ,and 999, surveying Entering data into a geographic information system, search and rescue , Geophysical Sciences, Tracking devices used in wildlife management

Current and proposed satellite navigation systems

GPS
The best known satellite navigation system is the US' Global Positioning System (GPS). This consists of many satellites that orbit in six different planes.

Galileo
The European Union and European Space Agency agreed on March, 2002 to introduce their own alternative to GPS, called Galileo. At a cost of about $2.5 billion dollars,

GLONASS
The USSR counterpart to GPS is called GLONASS and was used as a backup by some commercial GPS receivers.

EGNOS
As a precursor to Galileo, the European Space Agency, the European Commission and EUROCONTROL are developing the European Geostationary Navigation Overlay System (EGNOS).

Beidou
China has started to launch a series of satellites intended to form a system called the Beidou navigation system.

DORIS
DORIS (Doppler Orbitography and Radio-positioning Integrated by Satellite), French precision system.

Often the systems can be wrong they can give short cut ideas that are not appropriate for larger or less powerful transport. For instance one farmer once had to cope with large trucks driving throgh his farm, which would then get stuck once they reached the steep cliff like road, their system was expecting them to travail. Often many complain the sytem is difficult to learn.

Galileo is an incredibly important system for Europe and the UK is playing a very large role

THE GALILEO PROJECT

Europe's own global satellite navigation system
30 satellites in three medium-Earth orbits (23,600km)
Will work alongside US GPS and Russian Glonass systems
Promises real-time positioning down to under a metre
Performance improvements should see sat-nav expand into many more mobile devices
Suitable for safety-critical systems - can run trains, guide cars and land planes